....CH..............LI..NL......................................................JDIM350 (Ver 2.1 Jan 2001) 2100000/01278232EUROPEAN PATENT SPECIFICATIONB120041110EP02254979.4200207162002100420030328enenen90590620010717US200411102004462003012220030420041110200446200405197 7H 01L 21/00 A 7B 23K 20/00 BdeApparat und Methode zur Kontrolle der VerbindungskraftenApparatus and method for bond force controlfrAppareil et méthode de contrôle la force de soudureEP-A- 1 187 180US-A- 5 230 458US-A- 5 351 872PATENT ABSTRACTS OF JAPAN vol. 016, no. 462 (E-1269), 25 September 1992 (1992-09-25) & JP 04 162730 A (NEC KYUSHU LTD), 8 June 1992 (1992-06-08)3Wong, Sun Kuen20/F., Watson Centre, 16-22 Kung Yip St.Kwai Chung, Hong KongCNWan, Ming Yeung20/F., Watson Centre, 16-22 Kung Yip St.Kwai Chung, Hong KongCNASM Assembly Automation Ltd.03227931TLJ/1cs/EP16305Assembly Automation Ltd., ASM20/F., Watson Centre, 16-22 Kung Yip StreetKwai Chung, Hong KongCNJohnson, Terence Leslie00042961Marks & Clerk Incorporating Edward Evans Barker Clifford's Inn, Fetter LaneLondon EC4A 1BZGBCHLINL20030502200318

This invention relates to an apparatus and method for bond force control, and in particular to such control in a die bonding operation.

In a die bonding operation in a semiconductor assembly and manufacturing process, a bond head may pick a die (which may be an electronic device such as a semiconducting integrated circuit device) at a first location and will move the die to a second location at which the die is to be bonded to a substrate, such as a circuit board. The bond head will then move downwardly (this is known as the z-direction) until the die touches the substrate. In order to apply a required bond force during the bond operation, the bond head may be driven downwardly further to exert a required force on the die.

Apparatus and methods for controlling this bond force need to meet a number of conflicting requirements. For example, they should preferably be able to apply a bond force over a wide range, should be susceptible to feedback and control, and should be able to respond rapidly to required changes in the bond force.

To date prior art techniques have failed to satisfactorily meet all the requirements for ideal bond force control. Conventionally bond force control is achieved using a compression spring, or a pneumatic actuator, or a solenoid, and a number of examples of such conventional prior art bond force control techniques will now be shown.

Fig.1 shows a compression spring type system. In such a system a compression spring 1 is mounted within the bond head 3 and exerts a force on a movable assembly 2 that connects to a collet bearing the die. In a die bonding process a die will be held (for example by vacuum) to a collet formed as part of the movable assembly 2. The bond head is moved downwardly in the z-direction until the die touches the substrate. In order to exert a bonding force the bond head 3 continues to move in the z-direction so as to compress the spring 1 against the movable assembly 2 and to exert a bond force on the die through the collet.
In order to avoid excess vibrations of the movable assembly 2 during motion of the bond head 3, the spring 1 is usually preloaded and the amount of preload directly affects the minimum bond force that can be applied. The larger the preload, the larger is the minimum bond force that can be applied. This is because when the collet and die touch the substrate (which is a rigid surface), the reaction force that pushes the collet and die against the spring should be larger than the preload of the spring. This means that if a very small bond force is required, the preload of the spring must also be very small, but this in turn has the disadvantage of resulting in more vibrations of the bond head following movement which will thus require a longer settling time in the bonding operation.

Another problem that arises from simply reducing the preload of the spring to enable a small bonding force to be applied, is that the contact of the spring with the movable assembly 2 and the bond head housing 3 may be poor and the bond force may be non-linear. This can be mitigated by reducing the spring constant k so that a larger extent of compression, good contact, and small preload can all be obtained at the same time. The price for this, however, is that the range of the output force produced by the spring is reduced and this method can only really work with small bond force applications.

US 5950903 discloses a system similar to the use of a compression spring, but using a leaf spring instead of a compression spring.

Fig.2 shows a schematic of a prior art example that uses a pneumatic actuator instead of a compression spring. A pressure chamber 4 is provided within the bond head housing 6 and acting upon the movable collect assembly 5. In this arrangement a variable bond force can be applied by controlling the pressure within the pressure chamber 4. A difficulty with this design, however, is that the response time is slow. If the pressure in the chamber 4 is controlled using a pressure regulator the response time is too slow for a real time closed loop control system and instead an open loop control is used instead. A related disadvantage is that there is a relatively large impact force. At the moment that the die touches the substrate surface an impact force is produced that acts upon the die. If this impact force is too large it can damage the die, but the slow response time of a pneumatic system makes it very difficult to control the impact force. It is also difficult to control the bond force with any great accuracy. In solenoid systems such as those described for example in US patents 3,727,822, 4,603,802, 5,230458 and 5,696,329 a solenoid is used in place of a compression spring or a pneumatic actuator to provide the bond force. Solenoid systems have a number of advantages, including fast response times, the ability to incorporate closed-loop control, and easy accurate control. The main disadvantage, however, is that the output bond force is relatively small, and to create a large bond force when such is required, a large and correspondingly heavy solenoid must be used. Generally, solenoid systems are only suitable for use in applications where a small bond force is required.

JP 04 162730 relates to a die-bonding apparatus in which a bond force is controlled by changing the amount of displacement/compression of the spring when the spring is in contact with and pressing against a die. To increase the bond force, a motor presses the spring further against the die, and vice versa.

It is an object of the invention to seek to provide an apparatus and method for providing bond force control that facilitates the generation of a bond force over a wide range of values, allows fast response and closed loop control, and is simple in design and construction.

According to a first aspect of the present invention there is provided die-bonding apparatus for providing a desired bond force in a die bonding operation, the apparatus comprising means for generating a primary bond force, characterised in that the apparatus further comprises means for generating a secondary bond force, and means for controlling the secondary bond force, whereby a desired bond force, which comprises the sum of the primary bond force and the secondary bond force, may be provided.

According to a second aspect of the present invention there is provided a method of generating a desired bond force in a die bonding operation, comprising providing a primary bond force, characterised in that the method further comprises generating a secondary bond force in the same direction or opposite to said primary bond force, summing said primary bond force and said secondary bond force to generate said bond force, and controlling the magnitude and sign of said secondary bond force, whereby a desired bond force may be provided.

According to a third aspect of the present invention there is provided a method of generating a desired impact force in a die bonding operation, comprising moving a bond head bearing a die toward a substrate in a first direction, characterised in that the method further comprises generating a secondary force in a direction opposite to said first direction at the moment of impact of said die on said substrate, and controlling the magnitude and sign of said secondary force, whereby a desired impact force may be provided.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:-

An embodiment of the present invention will now be described with reference to Figs.3 and 4. As will be seen in more detail from the following description, an important aspect of the present invention is that the apparatus and method involves the provision of a first primary bond force generating means such as a compression spring, and a second bond force generating means that is capable of rapidly and accurately generating a secondary bond force that may be positive or negative to provide fine control of the primary bond force. This secondary bond force may be generated, for example, by a motor.

Referring to Figs.3 and 4, a bond head according to an embodiment of the invention comprises a bracket 10 for supporting the bond force generating means. The primary bond force generating means comprises a compression spring 11 fixed between one end of a shaft 12 and a mount 25 for a bond force motor coil to be described below. Compression spring 11 is provided with a preload P and can act upon a collet assembly 14 and die 15 through a slider mount 16. A force sensor 17 is located between the slider mount 16 and the collet assembly 14. Collet assembly 14 is fixed to slider mount 16 which is formed with bearings 18 that allow the slider mount 16 to slide relative to sliders 19 two of which are formed parallel to the axis of the spring 11, slider mount 16, force sensor 17 and collet assembly 14 (this axis lying on the z-direction). It will thus be understood that the collet assembly 14 may slide relative to the bracket 10 in the z-direction. Collet assembly 14 is adapted to pick and hold a semiconductor die 15 by suction.

A secondary bond force generating means is provided in the form of a bond force motor comprising an annular magnet 21 surrounding the spring 11 and sandwiched between a ferromagnetic core 22 and a ferromagnetic plate 23. A bond force motor coil 24 is supported on coil mount 25 and is provided in the annular space defined between the edge of the plate 23 and a downwardly extending annular flange portion of the core 22. It will be understood that by the application of a current to the motor coil 24 a force may be generated in the z-direction that acts upon the collet assembly 14. Depending on the direction of the current flow in the coil 24, this force may be positive (ie downwardly in the z-direction towards the substrate) and will act in addition to the compression spring, or may be negative (ie upwardly in the z-direction away from the substrate) and will act against the compression spring. As will be seen from the following, the current applied to the coil 24 may be controlled in response to the output of the force sensor to provide a closed loop control of the bond force.
The operation of the embodiment of the present invention will now be described in situations (a) where a small bond force is required, and (b) where a large bond force is required.

It will be understood that to begin with the bond head is moved to a location to pick a semiconductor die. The die may be held to the collet assembly 14 by vacuum in a conventional manner and is carried to a boding location where the die is to be bonded to a substrate. The bond head is then moved downwardly in the z-direction until the die touches the substrate. This point can be detected by the force sensor.

The first situation (a) may be considered to be described by the equation F < Fmmax + P where F is the required bond force, P is the preload of the compression spring and Fmmax is the maximum force generated by the bond force motor. In this situation the bond force can be controlled solely by varying the output of the bond force motor by varying the current applied to the motor coil. In particular, if the required bond force is greater than the preload of the compression spring, a positive force Fm may be generated by the bond force motor that acts in addition to the preload P of the spring to provide the required bonding force. The force sensor can be used to provide a feedback control of the current supplied to the coil so that the bond motor force is accurately controlled which in turn will accurately control the bond force. Similarly if the required bond force F is smaller than the preload P of the spring, this can be achieved by supplying an opposite current to the bond force motor coil so that the bond force motor generates a negative force that acts upwardly against the compression spring. Again this negative bond motor force can be accurately controlled by a closed loop control using the force sensor.

Situation (b) may be considered to be represented by the equation F ≥ Fmmax + P. In this situation the required bond force is obtained by controlling the force Fm of the bond force motor and the force Fs generated by the spring. The force generated by the bond force motor is controlled by supplying a current to the motor coil as discussed above. The force generated by the spring is controlled by moving the bond head further downwardly towards the substrate surface. The collet assembly and die cannot move any further, and therefore there is a relative movement z of the collet assembly and die in the direction of the arrow A in Fig. 4 that serves to compress the spring by a distance z and the force generated by the spring will increase to P + kz where k is the spring constant of the spring. Thus the total bond force is Fm + P + kz and this can be controlled rapidly and accurately by varying the current to the motor coil to change Fm in response to closed loop control from the force sensor.

In practice the situations (a) and (b) may not always be clearly defined and the border between them may be unclear. In particular the methodology of (b), in which the spring force component is increased by driving in the bond head, may also be applied in scenario (a).

It will be understood that in this embodiment of the present invention there is provided a primary bond force generating means in the form of the compression spring (though this could be replaced by a leaf spring or by a pneumatic actuator). In addition, however, there is also provided a secondary bond force generating means in the form of a bond force motor. The compression spring provides the main element of the bond force with all the advantages of a compression spring (simple construction, large available range of bond force), but the addition of a positive or negative secondary bond force from the bond force motor allows the total bond force to be rapidly and accurately controlled by means of a closed loop control of the current supplied to the motor coil.

It should also be noted that in addition to providing accurate control of the bond force in both small and high bond force applications, a further advantage of the present invention is that it allows the impact force to be minimized. This can be achieved by allowing the bond force motor to generate a negative bond force at the moment of impact and before the bonding process is commenced. In addition, another advantage is that vibration of the bond head during movement can be reduced using the embodiment of the invention. In particular during movement of the bond head (either in the z direction prior to engaging the substrate) or when moving in the x and y directions to pick a die and to carry it to the bonding location, vibrations of the collet assembly within the bond head can be reduced by using the bond force motor to generate a negative bond force that causes the collet assembly to move upwardly relative to the remainder of the bond head as far as it can until it reaches a stop position.

 Die-bonding apparatus for providing a desired bond force in a die bonding operation, the apparatus comprising means (11) for generating a primary bond force, characterised in that the apparatus further comprises means (21,24) for generating a secondary bond force, and means (17) for controlling the secondary bond force, whereby a desired bond force, which comprises the sum of the primary bond force and the secondary bond force, may be provided. Apparatus as claimed in claim 1, wherein said secondary bond force may be directed either in the same direction as the primary bond force or in the opposite direction to the primary bond force. Apparatus as claimed in claim 1 or claim 2, wherein the primary bond force generating means comprises a compression spring, a leaf spring or a pneumatic actuator. Apparatus as claimed in claim 3, wherein said primary bond force generating means comprises a preloaded compression spring (11). Apparatus as claimed in any preceding claim, wherein the secondary bond force generating means comprises a motor (21,24). Apparatus as claimed in any preceding claim, further comprising a force sensor (17) for sensing the applied bond force, and for producing an output for controlling the secondary bond force generating means. Apparatus as claimed in any preceding claim, wherein said primary bond force generating means (11) is movable relative to a die holding means (10) whereby the bond force component provided by said primary bond force generating means (11) is variable by moving said primary bond force generating means relative to said die holding means (10). Apparatus as claimed in claims 5-7 wherein said primary bond force generating means comprises a spring (11), and the motor includes a coil (24), and said apparatus further comprises a bond force sensor (17) for sensing the bond force and for controlling the said current applied to said coil (24) to maintain a desired bond force. A method of generating a desired bond force in a die bonding operation comprising providing a primary bond force, characterised in that the method further comprises generating a secondary bond force in the same direction or opposite to said primary bond force, summing said primary bond force and said secondary bond force to generate said bond force, and controlling the magnitude and sign of said secondary bond force, whereby a desired bond force may be provided. A method as claimed in claim 9 comprising sensing an instantaneous bond force, and controlling said secondary bond force in response to said sensed instantaneous bond force. A method as claimed in claim 9 or claim 10, wherein said primary bond force is provided by means of a compression spring (11), a leaf spring or a pneumatic actuator. A method as claimed in any of claims 9 to 11, wherein said secondary bond force is provided by means of a motor (21,24). A method as claimed in claim 12 wherein the motor (21,24) comprises a motor coil (24), and wherein the magnitude and sign of said secondary force is controlled by varying the magnitude and direction of a current applied to said coil. A method as claimed in any of claims 9 to 13, wherein said primary bond force comprises a preload component, and wherein the generated bond force comprises the sum of said preload component and said secondary bond force. A method as claimed in any of claims 9 to 14, wherein said primary bond force comprises a preload component and a variable component, and wherein the generated bond force comprises the sum of said preload component, said variable component and said secondary bond force. A method of generating a desired impact force in a die bonding operation, comprising moving a bond head bearing a die (15) toward a substrate in a first direction, characterised in that the method further comprises generating a secondary force in a direction opposite to said first direction at the moment of impact of said die (15) on said substrate, and controlling the magnitude and sign of said secondary force, whereby a desired impact force may be provided. Druckbondierungsvorrichtung zum Bereitstellen einer erwünschten Bondierungskraft in einem Druckbondierungsvorgang, wobei die Vorrichtung eine Einrichtung (11) zum Erzeugen einer primären Bondierungskraft umfasst, dadurch gekennzeichnet, dass die Vorrichtung außerdem eine Einrichtung (21, 24) zum Erzeugen einer sekundären Bondierungskraft und eine Einrichtung (17) zum Steuern der sekundären Bondierungskraft umfasst, wodurch eine gewünschte Bondierungskraft, welche die Summe aus der primären Bondierungskraft und der sekundären Bondierungskraft umfasst, bereitgestellt werden kann. Vorrichtung nach Anspruch 1, wobei die sekundäre Bondierungskraft entweder in derselben Richtung wie die primäre Bondierungskraft oder in der Richtung entgegengesetzt zu der primären Bondierungskraft, ausgerichtet ist. Vorrichtung nach Anspruch 1 oder 2, wobei die primäre Bondierungskrafterzeugungseinrichtung eine Druckfeder, eine Blattfeder oder ein pneumatisches Stellorgan umfasst. Vorrichtung nach Anspruch 3, wobei die primäre Bondierungskrafterzeugungseinrichtung eine vorgespannte Druckfeder (11) umfasst. Vorrichtung nach einem der vorangehenden Ansprüche, wobei die sekundäre Bondierungskrafterzeugungseinrichtung einen Motor (21, 24) umfasst. Vorrichtung nach einem der vorangehenden Ansprüche, außerdem aufweisend einen Kraftsensor (17) zum Erfassen der angelegten Bondierungskraft und zum Erzeugen eines Ausgangssignals zum Steuern der sekundären Bondierungskrafterzeugungseinrichtung. Vorrichtung nach einem der vorangehenden Ansprüche, wobei die primäre Bondierungskrafterzeugungseinrichtung (11) relativ zu einer Druckhalteeinrichtung (10) beweglich ist, wodurch die Bondierungskraftkomponente, welche durch die primäre Bondierungskrafterzeugungseinrichtung (11) bereitgestellt ist, durch Bewegen der primären Bondierungskrafterzeugungseinrichtung relativ zu der Druckhalteeinrichtung (10) variabel ist. Vorrichtung nach einem der Ansprüche 5 bis 7, wobei die primäre Bondierungskrafterzeugungseinrichtung eine Feder (11) umfasst und der Motor eine Wicklung (24) umfasst, und wobei die Vorrichtung außerdem einen Bondierungskraftsensor (17) zum Erfassen der Bondierungskraft und zum Steuern des an die Spule (24) angelegten Stroms zur Aufrechterhaltung einer erwünschten Bondierungskraft umfasst. Verfahren zum Erzeugen einer erwünschten Bondierungskraft in einem Druckbondierungsvorgang, aufweisend das Bereitstellen einer primären Bondierungskraft, dadurch gekennzeichnet, dass das Verfahren außerdem das Erzeugen einer sekundären Bondierungskraft in derselben Richtung oder entgegengesetzt zu der primären Bondierungskraft umfasst, das Summieren der primären Bondierungskraft mit der sekundären Bondierungskraft zur Erzeugung der Bondierungskraft, und das Steuern der Höhe und des Vorzeichens der sekundären Bondierungskraft, wodurch eine erwünschte Bondierungskraft bereitgestellt werden kann. Verfahren nach Anspruch 9, außerdem aufweisend das Erfassen einer momentanen Bondierungskraft und das Steuern der sekundären Bondierungskraft in Reaktion auf die erfasste momentane Bondierungskraft. Verfahren nach Anspruch 9 oder 10, wobei die primäre Bondierungskraft bereitgestellt wird mittels einer Druckfeder (11), einer Blattfeder oder eines pneumatischen Stellorgans. Verfahren nach einem der Ansprüche 9 bis 11, wobei die sekundäre Bondierungskraft durch einen Motor (21, 24) bereitgestellt wird. Verfahren nach Anspruch 12, wobei der Motor (21, 24) eine Motorwicklung (24) umfasst, und wobei Höhe und Vorzeichen der sekundären Kraft gesteuert werden durch Variieren der Höhe und Richtung eines an die Wicklung angelegten Stroms. Verfahren nach einem der Ansprüche 9 bis 13, wobei die primäre Bondierungskraft eine Vorlastkomponente umfasst, und wobei die erzeugte Bondierungskraft die Summe aus der Vorlastkomponente und der sekundären Bondierungskraft umfasst. Verfahren nach einem der Ansprüche 9 bis 14, wobei die primäre Bondierungskraft eine Vorlastkomponente und eine variable Komponente umfasst, und wobei die erzeugte Bondierungskraft die Summe aus der Vorlastkomponente, der variablen Komponente und der sekundären Bondierungskraft umfasst. Verfahren zum Erzeugen einer erwünschten Stoßkraft in einem Druckbondierungsvorgang, aufweisend das Bewegen eines eine Stanze (15) umfassend Bondierungskopfs in Richtung auf ein Substrat in einer ersten Richtung, dadurch gekennzeichnet, dass das Verfahren außerdem das Erzeugen einer sekundären Kraft in einer Richtung entgegengesetzt zu der ersten Richtung zum Zeitpunkt des Stoßes der Stanze (15) auf das Substrat umfasst, und das Steuern der Höhe und des Vorzeichens der sekundären Kraft, wodurch eine erwünschte Stoßkraft bereitgestellt werden kann. Dispositif de liaison de puce pour la délivrance d'une force de liaison désirée au cours d'une opération de liaison de puce, le dispositif comprenant des moyens (11) pour générer une force de liaison primaire, caractérisé en ce que le dispositif comporte en outre des moyens (21, 24) pour produire une force de liaison secondaire, et des moyens (17) pour commander la force de liaison secondaire, qui permet d'obtenir une force de liaison désirée, qui comprend la somme de la force de liaison primaire et de la force de liaison secondaire. Dispositif selon la revendication 1, dans lequel ladite force de liaison secondaire peut être dirigée soit dans la même direction que la force de liaison primaire, dans la direction opposée à celle de la force de liaison primaire. Dispositif selon la revendication 1 ou la revendication 2, dans lequel les moyens de production de la force de liaison primaire comprennent un ressort de pression, un ressort à lame ou un actionneur pneumatique. Dispositif selon la revendication 3, dans lequel lesdits moyens de production de la force de liaison primaire comprennent un ressort de compression précontraint (11). Dispositif selon l'une quelconque des revendications précédentes, dans lequel les moyens de production de la force de liaison secondaire comprennent un moteur (21,24). Dispositif selon l'une quelconque des revendications précédentes, comprenant en outre un capteur de force (17) pour détecter la force de liaison appliquée et pour produire un signal de sortie pour commander les moyens de production de la force de liaison secondaire. Dispositif selon l'une quelconque des revendications précédentes, dans lequel lesdits moyens (11) de production de la force de liaison primaire sont déplaçables par rapport à des moyens (10) de retenue de puce, ce qui a pour effet que la composante de force de liaison fournie par lesdits moyens (11) de production de la force de liaison primaire est variable sous l'effet du déplacement desdits moyens de production de la force de liaison primaire par rapport auxdits moyens (10) de retenue de puce. Dispositif selon les revendications 5 à 7, dans lequel lesdits moyens de production de la force de liaison primaire comprennent un ressort (11), et le moteur inclut une bobine (24), et ledit dispositif comprend en outre un capteur (17) de la force de liaison servant à détecter la force de liaison pour commander ledit courant appliqué à ladite bobine (24) pour maintenir une force de liaison désirée. Procédé pour produire une force de liaison désirée dans une opération de liaison de puce comprenant la délivrance d'une force de liaison primaire, caractérisé en ce que le procédé comprend en outre la production d'une force de liaison secondaire dans la même direction que ladite force de liaison primaire ou dans la direction opposée à cette force, l'addition de ladite force de liaison primaire et de ladite force de liaison secondaire pour produire ladite force de liaison, et la commande de l'amplitude et du signe de ladite force de liaison secondaire, qui permet de produire une force de liaison désirée. Procédé selon la revendication 9, comprenant la détection d'une force de liaison instantanée et la commande de ladite force de liaison secondaire en réponse à ladite force de liaison instantanée détectée. Procédé selon la revendication 9 ou la revendication 10, selon lequel ladite force de liaison primaire est produite au moyen d'un ressort de pression (11), d'un ressort à lame ou d'un actionneur pneumatique. Procédé selon l'une quelconque des revendications 9 à 11, selon lequel ladite force de liaison secondaire est fournie au moyen d'un moteur (21, 24). Procédé selon la revendication 12, selon lequel le moteur (21, 24) comprend une bobine (24) du moteur, et selon lequel l'amplitude et le signe de ladite force secondaire sont commandés par modification de l'amplitude et la direction d'un courant appliqué à ladite bobine. Procédé selon l'une quelconque des revendications 9 à 13, selon lequel ladite force de liaison primaire comprend une composante de précontrainte, et selon lequel la force de liaison produite comprend la somme de ladite composante de précontrainte et de ladite force de liaison secondaire. Procédé selon l'une quelconque des revendications 9 à 14, dans lequel ladite force de liaison primaire comprend une composante de précontrainte et une composante variable, et selon lequel la force de liaison produite comprend la somme de ladite composante de précontrainte, de ladite composante variable et de ladite force de liaison secondaire. Procédé pour produire une force d'impact désirée dans une opération de liaison de puce comprenant le déplacement d'une tête de liaison portant une puce (15) en direction d'un substrat dans une première direction, caractérisé en ce que le procédé comprend en outre la production d'une force secondaire dans une direction opposée à ladite première direction au moment de l'impact de ladite puce (15) sur ledit substrat, et la commande de l'amplitude du signal de ladite force secondaire de manière à pouvoir produire une force d'impact désirée.